Advanced Topics › z/VM Considerations › Telling z/VM to Send Reserve CCWs to Devices

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Telling z/VM to Send Reserve CCWs to Devices

If z/VM is not sending reserve and release CCWs to your devices, then take additional steps to make z/VM send these CCWs to your devices. This ensures that access is serialized among real processors. To make z/VM forward reserve CCWs temporarily (that is, until the next time you perform an IPL), issue a SET SHARED command for that device. Specify the address of the device as a parameter on the command. For example, to make z/VM send reserve CCWs to device 123, issue this Class B command:

SET SHARED ON FOR 123

To make z/VM forward reserve CCWs permanently, specify SHARED=YES on the RDEVICE macro in the HCPRIO assembly file, or SHARED YES on the RDEVICE macro in the system configuration file. Repeat this step for each shared device. Your changes to the RDEVICE macro take effect the next time you perform a system generation and IPL for z/VM.